1. Field of the Invention
The present invention relates to a stereoscopic image displaying method and a stereoscopic image displaying apparatus and, more particularly, to those capable of displaying an ordinary two-dimensional image and a stereoscopic image on a switched basis or capable of displaying a two-dimensional image and a stereoscopic image on a mixed basis, which are suitably applicable to observation of a stereoscopic image on TV, video, computer monitors, game machines, and so on.
2. Related Background Art
There is a conventional, stereoscopic image displaying method for preparing different polarization states for parallax images for the right eye and for the left eye and separating the left and right parallax images from each other by use of polarizing glasses. In the method under practical use, a liquid crystal shutter is provided on the display device side in order to prepare the different polarization states, the polarization states are switched one after the other in synchronism with field signals of display images on the display device, and an observer wearing the polarizing glasses can observe a stereoscopic image by separately viewing the left and right images in time division by the respective eyes. This method, however, had a drawback in that the observer always had to wear the polarizing glasses, which was troublesome.
Aside from the above method, the so-called parallax barrier method is known as one of stereoscopic image displaying method that does not require special glasses as the polarizing glasses. The parallax barrier method is a method for placing a barrier, for example, before or after the display device to spatially separate the images entering the left and right eyes from each other.
FIG. 12 is a perspective view of a major part of a stereoscopic image displaying apparatus suggested in Japanese Laid-open Patent Application No. 9-304739.
In the same figure, the apparatus has a surface illuminant, a transmissive display device, and a barrier (mask) having a plurality of apertures. The display device is adapted to display a stripe image, the stripe image being one image obtained by dividing each of the parallax image for the right eye and the parallax image for the left eye into stripes to obtain right stripe pixels and left stripe pixels and alternately arranging the right stripe pixels and left stripe pixels, thus obtained, in a predetermined order. The spatial relation between the apertures of the mask pattern and the stripe pixels is adapted to separate light beams emerging from the surface illuminant and then passing through the apertures and through the left or right stripe pixels, into different regions, thus permitting the observer to visually observe the stereoscopic image.
In the drawing, reference numeral 6 designates a transmissive liquid crystal display (display device) for displaying the image, which is constructed in such structure that a display surface (display pixel portion) 1 of a liquid crystal layer is interposed between two glass substrates 5. It is noted that the elements including a polarizing plate, a color filter, electrodes, a black matrix, and an antireflection film are omitted from the illustration.
Numeral 10 denotes a back light (surface illuminant) as an illumination light source. Numeral 7 represents a mask substrate (mask), which is made of glass or plastic and which is disposed opposite to a light-emitting surface of the back light 10. A mask pattern 9 having checkered apertures (apertures A) 8 for transmitting light, is formed in the surface of the mask 7. The mask pattern 9 is made of a metal deposit film of chromium or the like, or a light absorbing material, and is made on the mask substrate 7 by patterning. The mask substrate 7 functions as a mask having the checkered apertures 8 formed therein.
Numeral 4 indicates a lenticular lens (cylindrical lens array), which is made of a transparent plastic or glass in an array structure in which many cylindrical lenses, each being comprised of a flat surface and a convex cylindrical surface and extending in the vertical direction, are arrayed in the horizontal direction. This lenticular lens 4 is disposed between the mask substrate 7 and the liquid crystal display 6. The lens curvature of the lenticular lens 4 is set so that the mask pattern 9 is located approximately at the focus position of the cylindrical lenses composing the lenticular lens 4. A horizontal string of apertures 8 of the mask pattern 9 corresponds to each cylindrical lens forming the lenticular lens 4.
Numeral 2 represents a light directivity control element, which is made of polymer distributed liquid crystal (PDLC) and which can control either transmitting the incident light as it is or scattering it by an electric field applied thereto. Namely, the element 2 controls the directivity of the incident light. By controlling this light directivity control element 2 and the display image on the liquid crystal display 6, the stereoscopic image and the two-dimensional image are displayed on the switched basis or on the mixed basis.
FIG. 12 illustrates an example in which a stereoscopic image is displayed across the entire surface of the display surface 1. In this case, a system controller (not illustrated) or the like supplies a display control signal for displaying the stereoscopic image to apply a voltage through drive circuit 76 to the entire surface of the light directivity control element 2, so as to control the element 2 in a non-scattering state.
At the same time as it, the aforementioned display control signal is also input into image processing device 75, the image processing device 75 captures or produces the parallax image for the right eye (right parallax image) R and the parallax image for the left eye (left parallax image) L from a parallax image source not illustrated, the image processing device 75 divides each of the two parallax images into horizontal stripes to produce right stripe pixels R.sub.1 R.sub.2 R.sub.3 R.sub.4 . . . and left stripe pixels L.sub.1 L.sub.2 L.sub.3 L.sub.4 . . . , the image processing device 75 synthesizes one horizontal stripe image by alternately arranging them, for example, in the order of R.sub.1 L.sub.2 R.sub.3 L.sub.4 R.sub.5 L.sub.6 . . . from the top of the screen, and the device 75 outputs the image signal to a display drive circuit 73. The display drive circuit 73 receives the above signal to drive the liquid crystal display 6, so that the horizontal stripe image is displayed on the display surface 1 as shown in FIG. 12. Symbols E.sub.R, E.sub.L represent the right eye and the left eye, respectively, of the observer.
For displaying the two-dimensional image on the display surface 1, the voltage is not applied to the light directivity control element 2, so as to keep the element 2 in a scattering state. The display surface 1 is illuminated by scattered light at this time, so as to permit the observer to observe the two-dimensional image.
In the stereoscopic image displaying apparatus shown in FIG. 12, the light directivity control element 2 is made of the polymer distributed liquid crystal (PDLC). For displaying the stereoscopic image on the liquid crystal display (display surface), the voltage is applied to PDLC, so as to keep PDLC in the non-scattering state, whereby the incident light is transmitted as it is. For displaying the two-dimensional image on the display surface, the voltage is not applied to keep the liquid crystal in the scattering state, whereby the incident light is scattered. This is utilized to achieve changeover between the stereoscopic image display and the two-dimensional image display.
During observation of the stereoscopic image, however, a small quantity of scattered light sometimes comes out of the polymer distributed liquid crystal (PDLC) even with application of the voltage thereto because of the property of PDLC. This sometimes increases crosstalk, so as to degrade the observation condition of the stereoscopic image.